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Diamonds Aren’t Forever

By Debra Meiburg MW

A certain platinum blond would have you believe that diamonds are a girl’s best friend, and many wine connoisseurs would agree. However, due to an unfortunate public misperception of these little gems, wine diamonds are increasingly rare these days. Wine diamonds or weinstein – wine stones in German – are the small, mostly-clear crystals sometimes found clustered on corks or sparkling in the base of your wine.

These glittering diamonds are actually tartrate crystals, derived from tartaric acid, a natural component of grapes and many other fruits including bananas and tamarind. The tartaric acid precipitates or “falls out” in a crystallized state when wine is chilled to a low temperature. In northern European wine regions these crystals form naturally while the wine matures during long chilly winters. Later, during the warmer spring and summer months, the wine is lightly filtered to prevent loose crystals from entering the bottles, and cellar hands begin scraping away tartrate crystals still clinging to the insides of barrels and tanks. The scrapings are subsequently ground into cream of tartar, a baking ingredient familiar to anyone who makes meringues, soufflés or angel food cakes.

Because this crystallization does not occur naturally in warmer wine regions, the precipitation may inadvertently take place after bottling, say in the chilly cargo hold of an airplane – or on overly cool refrigeration racks. Unwilling to take the risk that their wines hit the shelves looking like they were dressed by de Beers, most winemakers spend a large amount of effort and money to try to prevent these crystals from forming.

Interestingly, opinions are divided as to whether the presence of wine diamonds is advantageous or unfavorable. Though harmless, consumers unused to tartaric acid sediment can find it unattractive or even hazardous, mistaking it for glass shards. As such, many winemakers artificially induce crystal formation before bottling by a technique called cold stabilization, whereby the wine is rapidly chilled for a brief period and then filtered. Other techniques include chemical additions to “seed” the crystals (think of it as like dropping a grain of sand into an oyster to start a pearl). The opposing camp of winemakers are adamantly against cold stabilization, arguing it alters the wine’s structure and causes unfavorable changes in character. This group are actually quite proud of their wine diamonds, seeing them as evidence of minimal intervention (they would say “manipulation”).

An intriguing possible link between wine diamonds and quality has to do with ripeness levels. As well as tartaric acid, wine also contains a sharper, greener acid called malic acid (also found in green apples). While the levels of tartaric acid stay the same more or less the same throughout the ripening process, malic acid levels drop as grapes get riper, resulting in a higher ratio of tartaric acid to malic acid. The presence of malic acid tends to slow down the formation of wine diamonds. Thus in the chilly Germany of yesteryear, where the grapes had difficulty reaching maturity and lower malic acid levels at harvest were desirable, wine diamonds were a reasonable indicator that the grapes were fully ripe at harvest. As a result, some traditional European connoisseurs actually seek out bottles with wine stones, particularly in older wines. On the flip side, in warmer regions that need sufficiently high acidity levels to keep their wines refreshing many minimalist winemakers avoid cold stabilization, which reduces precious acidity, banking on their consumers to understand if diamonds appear.

Whether or not they are a sign of quality is up for debate, but more important to acknowledge is that wine diamonds are harmless. So toss a few German Rieslings into your refrigerator this summer without fear (though we expect you’ll have quaffed them long before the wine diamond train arrives). Pink diamonds fans might try stocking their fridges with rosé. Ruby lovers can opt for red wines long-matured in cool cellars. Whatever your preference, be aware that tartrates are water soluble and most will dissolve in your mouth – proving what we knew all along. Diamonds aren’t forever.